Cable backplane

ABSTRACT

A main unit of a director-class switch including a wire-based backplane located in a chassis, having a plurality of slots configured to receive switch boards. The wire-based backplane includes a plurality of harnesses each including first and second cartridges, a plurality of interface port units mounted on each of the first and second cartridges and cables connecting each of the interface port units of the first cartridge to each of the interface port units of the second cartridge. The harnesses are mounted in the chassis such that the interface port units face ends of the slots in a manner configured to mate with corresponding connectors of switch boards inserted into the slots. A plurality of interface port units are mounted in each slot. Each cartridge includes interface port units which are located in a plurality of different slots.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/445,079 filed Jul. 29, 2014.

FIELD OF THE INVENTION

The present invention relates generally to communication switches, andspecifically to switch backplanes.

BACKGROUND OF THE INVENTION

With the advance of computer networking, there is a need to connectlarger numbers of computing devices. Switches are normally used toconnect computing devices, and when a large number of computing devicesneed to be connected to each other, large switches are utilized.

Director-class switches are used at the center of very large switchedfabrics. Such director-class switches are formed of a large number ofleaf boards which include ports for connecting to external equipment andspine boards which connect the leaf boards to each other within thedirector-class switch. In the prior art, director-class switches includea printed circuit board (PCB) backplane connecting the leaf and spineboards.

It is desirable to increase the number of ports serviced by adirector-class switch. The manufacture of large switches whichinterconnect hundreds of ports, such that each port is connected to alarge group of the other ports, is, however, a demanding task.

US patent publication 2014/0056174 to Walden et al., the disclosure ofwhich is incorporated herein by reference in its entirety, describesconnecting intelligent service modules external to a director-levelswitch, in order to avoid consuming the limited number of ports in adirector-level switch.

U.S. Pat. No. 6,504,841 to Larson et al., the disclosure of which isincorporated herein by reference in its entirety, describes a scalablecomputer interconnect using flexible ribbon cable connection.

U.S. Pat. No. 7,706,361 to McMillen et al., the disclosure of which isincorporated herein by reference in its entirety, describes a multistageinterconnect network in which signal wires are grouped intomulticonductor cables to minimize the number of handled cables.

SUMMARY OF THE INVENTION

Embodiments of the present invention that are described hereinbelowprovide a director-class switch, in which the backplane is formed fromwires grouped together in bundles.

There is therefore provided in accordance with an embodiment of thepresent invention a main unit of a director-class switch, comprising achassis, a plurality of slots on the chassis configured to receiveswitch boards; and a plurality of harnesses comprising first and secondcartridges, a plurality of interface port units mounted on each of thefirst and second cartridges and cables connecting each of the interfaceport units of the first cartridge to each of the interface port units ofthe second cartridge. The harnesses are mounted in the chassis such thatthe interface port units face ends of the slots in a manner configuredto mate with corresponding connectors of switch boards inserted into theslots. A plurality of interface port units are mounted in each slot, andeach cartridge includes interface port units which are located in aplurality of different slots.

Optionally, the plurality of slots are located on first and secondopposite walls of the chassis.

Optionally, the slots located on the first wall are configured toreceive boards of a single type.

Optionally, the slots located on the first wall are configured toreceive a different type of boards from the slots located on the secondwall. Optionally, the first and second opposite walls of the chassis areconnected by screws located in holes at least 50% larger than thecross-sections of the screws.

Optionally, each slot includes a plurality of interface port units ofdifferent harnesses.

Optionally, the plurality of harnesses include harnesses havingdifferent cables of different lengths allowing for different maximaldistances between the cartridges of the harness.

The main unit optionally includes a printed circuit board serving as aconnection between a power source of the director-class switch and powersockets in each of the slots.

Optionally, the main unit includes power cables connecting a powersource of the director-class switch to power sockets in each of theslots.

There is further provided in accordance with an embodiment of thepresent invention, a method of constructing a main unit of adirector-class switch, including providing a chassis including aplurality of slots on the chassis configured to receive switch boards,providing a plurality of harnesses including first and secondcartridges, a plurality of interface port units mounted on each of thefirst and second cartridges; and cables connecting each of the interfaceport units of the first cartridge to each of the interface port units ofthe second cartridge, mounting the harnesses in the chassis such thatthe interface port units face ends of the slots in a manner configuredto mate with corresponding connectors of switch boards inserted into theslots, a plurality of interface port units are mounted in each slot, andeach cartridge includes interface port units which are located in aplurality of different slots.

Optionally, providing the chassis comprises providing a chassis withwalls connected to each other in a manner allowing limited relativemovement.

Optionally, the method includes strengthening a connection between thewalls, limiting the possibility of relative movement of the walls, aftermounting the harnesses in the chassis.

Optionally, the plurality of harnesses includes harnesses havingdifferent cables of different lengths allowing for different maximaldistances between the cartridges of the harness.

Optionally, the harnesses all include the same number of interface portunits. Optionally, each of the cartridges of the harnesses comprises atleast four interface port units.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a director-class switch, in accordance withan embodiment of the present invention;

FIG. 2 is a schematic view of a director-class switch, in accordancewith an embodiment of the invention;

FIG. 3 is a view of a backplane cage of a director-class switch, inaccordance with an embodiment of the invention;

FIG. 4 shows a harness used as a building block of a backplane of adirector-class switch, in accordance with an embodiment of theinvention;

FIG. 5 is a schematic view of a harness within a backplane cage, inaccordance with an embodiment of the invention;

FIG. 6 is a diagram of the connections of a harness based backplane, inaccordance with an embodiment of the invention;

FIG. 7 is a schematic side view of a partial director-class switchbackplane within a cage, in accordance with an embodiment of theinvention;

FIG. 8 is a schematic top view of a cage of a director-class switchbackplane, with partial wiring of the backplane, in accordance with anembodiment of the invention; and

FIG. 9 is a flowchart of acts performed in assembling a director-classswitch, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention relate to a director-class switchhaving sub-switches connected to each other through a cable basedbackplane. The sub-switches belong to two sets, and the cable basedbackplane connects each sub-switch of one set to all the sub-switches ofthe other set. The cables of the backplane are grouped into groups ofcables connecting multi-sub-switch cartridges, such that the number ofconnections that need to be connected to form the backplane is on theorder of the number of cartridges rather than the number of cables. Thisreduces the amount of work required to form the backplane and simplifiesmaintenance and part replacement of the backplane, when necessary.

Optionally, the director-class switch also includes power cables whichconnect power sockets of boards on which the sub-switches are mounted toa central power supply of the director-class switch. Alternatively oradditionally, the director-class switch includes a cable-based controlbackplane which distributes control signals from a central controller ofthe switch to control sockets of the boards. The use of cables for thedistribution of power and/or control signals, although a PCB could beused, allows for more flexibility in the arrangement of the boards inthe switch chassis and thus reduces the extent of mechanical constraintson the connection of the cartridges to the boards. In some embodiments,the backplane uses cables for all connections and no PCBs are used toconnect different boards in the chassis. In addition, the use ofseparate cables for providing power to the boards, separates theelectric supply in a manner that reduces the chances that a short in oneboard will affect other boards.

An aspect of some embodiments of the invention relates to a multi-facedirector-class switch, including a plurality of slots for acceptingswitch boards, mounted on a plurality of faces of a backplane cage ofthe director-class switch. The backplane cage is constructed with someleeway between at least two of the faces of the cage, which carry switchboards. Accordingly, mechanical constraints induced by inserting switchboards into slots of a first face of the cage, do not induce substantialconstraints on slots of a second face.

System Overview

FIG. 1 is a block diagram of a director-class switch 100, in accordancewith an embodiment of the present invention. Director-class switch 100comprises a plurality of leaf switches 102, which each connects aplurality of external ports 104 to each other and to one or moreinternal ports 106. External ports 104 are adapted for connection toexternal devices (not shown), such as servers, computers, switchesand/or storage units. Generally, the leaf switches 102 are mounted inpairs on respective leaf boards 118, although in some embodiments eachleaf board carries only a single leaf switch, and in other embodimentsthree or more leaf switches 102 are mounted on each leaf board 118.

Switch 100 further comprises a plurality of spine boards 112, which eachhas a respective spine switch (not shown) which inter-connects aplurality of spine ports 114. A backplane 130 formed of cables, connectseach leaf switch 102 to each spine board 112. Optionally, each leafswitch 102 includes a number of internal ports 106 equal to the numberof spine boards 112 and each spine board 112 has a number of spine ports114 equal to the number of leaf switches 102. Alternatively, one ormore, possibly all, of leaf switches 102 and/or spine boards 112 mayhave extra ports for redundancy.

In one non-limiting example, switch 100 includes 36 leaf switches 102,mounted on 18 switch boards 118. Each of leaf switches 102 has 18internal ports 106, such that switch 100 includes 648 internal ports106. Switch 100 includes 18 spine boards 112, each of which includes 36spine ports 114, such that together switch 100 includes 648 internalports 106. It is noted that switch 100 may be designed for other, largeror smaller, numbers of boards, leaf switches and ports.

Switch Frame Structure

FIG. 2 is a schematic view of a main unit chassis 200 of director-classswitch 100 (FIG. 1), in accordance with an embodiment of the invention.Main unit chassis 200 comprises a central backplane cage 230, a spinebasket unit 208 and a leaf basket unit 236. Spine basket unit 208includes a plurality of spine slots 202 for receiving spine boards 112(FIG. 1). Leaf basket unit 236 includes a plurality of leaf slots 212,for receiving leaf boards 118 (FIG. 1). Optionally, spine basket unit208 is formed of a plurality of sub units 268, which are separatelyattached to backplane cage 230. Alternatively or additionally, leafbasket unit 236 is formed of a plurality of sub units 278, which areseparately attached to backplane cage 230.

Backplane cage 230 hosts backplane 130 (FIG. 1), as detailedhereinbelow. In some embodiments of the invention, power cables 288enter backplane cage 230 through a power slot 286. A top window 292 ofbackplane cage 230 is optionally used to pass control wires to the leafand/or spine boards.

Cage

FIG. 3 is a view of backplane cage 230, in accordance with an embodimentof the invention. A first wall 242 of cage 230 serves as a back wall ofspine slots 202 (FIG. 2) and a second wall 244 of cage 230 serves as aback wall of leaf slots 212 (FIG. 2). First wall 242 and second wall 244optionally each include a plurality of windows 302 and 304, throughwhich spine boards 112 (FIG. 1) and leaf boards 118 (FIG. 1) connect tointerface port units of backplane 130, as described hereinbelow. Cage230 further includes side walls 262, which connect first and secondwalls 242 and 244.

In some embodiments, cage 230 defines a narrow compartment 336 throughwhich power cables 288 connect to power sockets 326 that provide powerto leaf boards 118 and/or to power sockets on wall 244 that providepower to spine boards 112. Alternatively to passing the power cables ina separate compartment 336, the power cables pass in a main interior ofcage 230 along with the other wires forming backplane 130. The powerconnections are optionally passed over cables, similar to those used forbackplane 130, in order to minimize mechanical constraints ondirector-class switch 100. Alternatively, the power connections pass ona printed circuit board (PCB).

Walls 242 and/or 244 optionally define for each spine board 112 and/orleaf board 118, a respective control window 344 through which acontroller of the board (not shown) is connected to a control interface444 (FIG. 8), which in turn connects to control wires (not shown)passing through window 292. The control wires are optionally used toexchange control signals between the boards and a controller (not shown)of director-class switch 100.

In some embodiments of the invention, one or more of walls 242 and 244is formed of a plurality of separate units, connected to each other in amanner allowing additional leeway in connecting the boards 112 and/or118 to the walls 242 and/or 244. Cage 230 is optionally made of adurable material, such as aluminum or steel, which can withhold thepressures of boards being inserted into slots 202 and 212.

In some embodiments of the invention, the internal ports 106 of eachleaf switch 102 (FIG. 1) are divided into groups which connect to thewires of backplane 130 through separate windows 304. For example, theinternal ports 106 of each leaf switch 102 are optionally grouped intothree groups of six ports each, and each group connects to a respectiveleaf interface port unit 248 (FIG. 4) of the backplane. Similarly, thespine ports 114 of each spine board 112 (FIG. 1) are optionally dividedinto groups which connect to the wires of backplane 130 through separatewindows 302. For example, the spine ports 114 of each spine board 112are optionally grouped into six groups of six ports each, and each groupconnects to a respective spine interface port unit 246 (FIG. 4) of thebackplane.

It is noted that instead of side walls 262, cage 230 may include sidebars or other suitable connectors which connect walls 242 and 244.

Harnesses

In accordance with embodiments of the invention, the wires of backplane130 are constructed in separate modular harnesses, each of whichconnects a plurality of leaf interface port units 248 to a plurality ofspine interface port units 246 (FIG. 4). The use of separate harnessesto form the wire backplane 130 makes the construction of the backplanemuch simpler in a manner which reduces the chances of mistakes, makesthe assembly of the director-class switch simpler and allows easierreplacement of parts in case of a failure.

FIG. 4 shows a harness 400, in accordance with an embodiment of theinvention.

FIG. 5 is a schematic view of a harness 400 within cage 230, inaccordance with an embodiment of the invention. FIG. 5 shows thecontents of cage 230 after a single harness 400 is mounted within cage230.

Harness 400 comprises a plurality (e.g., six) of leaf interface portunits 248, to be mounted in respective windows 304 (FIG. 3), forconnecting to a plurality of respective leaf boards 102 (FIG. 1).

The leaf interface port units 248 are included together in a cartridge402 (e.g., a rod), allowing simple mounting thereof on wall 244 (FIG.3). A second cartridge 404 includes a plurality (e.g., six) of spineinterface port units 246, for connecting to a plurality of spine boards112 (FIG. 1). Harness 400 additionally includes cables 306, whichconnect each leaf interface port unit 248 in harness 400 to each of thespine interface port units 246 in harness 400.

The port connections of interface port units 246 and 248 are optionallymounted in the interface port units in a manner allowing them someleeway in movement, so as to allow adjustment to the ports of the boardsto which they are connected.

Cartridges 402 and 404 are optionally made of a rigid material, forexample a metal such as aluminum, iron or steel, in order to allow fordurability and withstand the pressures of inserting boards 112 or 118.Cartridges 402 and 404 are optionally at least 605, at least 70% or evenat least 80% metal. Alternatively, cartridges 402 and/or 404 comprise aplastic or other relatively elastic material which allows for resilienceto misalignment of different cards 102 and/or 112.

Interface port units 246 and 248 are optionally mounted on theirrespective cartridges 404 and 402 in a manner keeping the relativelocations of the interface port units on a single cartridge fixed.Alternatively, interface port units 246 and/or 248 are mounted on theircartridges in a manner leaving some leeway between the interface portunits on a single cartridge. The leeway is optionally achieved by usinga flexible material for cartridges 402 and/or 404 and/or by movablymounting the Interface port units 246 and 248 on their respectivecartridges.

Harness 400 of FIG. 4 is for connecting leaf interface port units 248and spine interface port units 246 of rows of the same height. Thedistance between cartridges 402 and 404 allowed by cables 306 isoptionally about the distance between walls 242 and 244.

FIG. 6 is a schematic spread-out diagram of the connections of backplane130, between walls 242 and 244, in accordance with an embodiment of theinvention.

Each group 610 of slots 304 (FIG. 3) for six leaf switches 102 isconnected on wall 244 by three harnesses to all 18 slots of spine boards112 on wall 242. Each harness is formed of a leaf cartridge 620 (marked620A, 620B, 620C, . . . ), a spine cartridge 622 (marked 622A, 622B,622C, . . . ) and cables 306 (FIG. 4), represented in FIG. 6 by a singleline 624.

Different harnesses optionally include cables of different lengths,depending on the relative intended positions of cartridges 620 and 622on walls 244 and 242, respectively. The three leaf cartridges 620Abelong to three harnesses in which they connect to three respectivespine cartridges 622A. Each of these three harnesses has cables of adifferent size. A first one of these harnesses connects a spinecartridge 622A and a leaf cartridge 620A at the same height. A secondone of these harnesses connects a spine cartridge 622A and a leafcartridge 620A six rows higher and one column aside, and optionally hascables sufficiently longer than the first harness to allow for passingthese six additional rows and one column. A third one of these harnessesoptionally connects a spine cartridge 622A and a leaf cartridge 620Atwelve rows higher and two columns to the side, and optionally hascables sufficiently longer than the first harness to allow for passingthese twelve additional rows and two columns to the side.

The three harnesses of cartridges 620B optionally include one which hascables for the same height and column as the middle row of cartridges622B, one for six rows higher and one column to the side and one for sixrows lower and one column to the side.

The three harnesses of cartridges 620C optionally include one which hascables for the same height and column as the bottom row of cartridges622C, one for six rows higher and one column to the side and one for sixrows lower and two columns to the side. The same harness lengthsconnecting cartridges 620A, 620B and 620C to cartridges 622A, 622B and622C, respectively, are optionally used for the harnesses connectingcartridges 620D, 620E and 620F to cartridges 622D, 622E and 622F.Accordingly, in some embodiments, the 18 harnesses forming backplane 130include harnesses of four different lengths:

1) same row and column;

2) six rows away and one column aside;

3) 12 rows away and two columns aside; and

4) six rows away and two columns aside.

It is noted, however, that other matchings of cartridges 620 and 622 maybe used, for example having the harness of same row cartridges 620B and622B be one or two columns aside, in which case more harness lengths arerequired. Further alternatively, a smaller number of harness lengths areused (e.g., three sizes, two sizes or only a single size), and, whennecessary, a longer size than necessary is used at the cost of havingslack wires within cage 230.

It is noted that in some embodiments, each leaf switch 102 and/or eachspine board 112 connects to a plurality of interface port units (246 or248), belonging to a plurality of different harnesses. In turn, theharnesses are each connected to a plurality of different boards (118 or112) and/or leaf or spine switches. While such connection scheme placesmechanical constraints on the harnesses and boards, the advantages offorming backplane 130 from prefabricated harnesses are considered inaccordance with embodiments of the invention to outweigh any possibledisadvantages of these constraints.

FIG. 7 is a schematic side view of a portion of backplane 130 withincage 230, in accordance with an embodiment of the invention. FIG. 7shows cage 230 after three columns of harnesses were mounted within cage230, while some of windows 302 and 304 are bare as their correspondingharnesses have not been mounted yet.

FIG. 8 is a schematic top view of cage 230 with partial wiring of thebackplane, in accordance with an embodiment of the invention. FIG. 8shows wires connecting only some of cartridges 402 and 404 in order toavoid over crowding of the figure.

Construction

FIG. 9 is a flowchart of a method of assembly of director-class switch100, in accordance with an embodiment of the invention. Optionally,spine basket unit 208, cage 230, leaf basket unit 236 and harnesses 400are manufactured separately and are collected (802) for assembly at anassembly location. In accordance with some embodiments of the presentinvention, side walls 262 are connected to walls 242 and 244 by screws270 (FIG. 3) positioned in holes 272 which are larger than thecross-sections of the screws, optionally by at least 25%, 50% or even100%. Optionally, when cage 230 is shipped to the assembly location,screws 270 are tightened such that side walls 262 are firmly attached towalls 242 and 244 without leeway, allowing safe shipment of cage 230.

In assembling director-class switch 100, screws 270 and walls 262 areopened (804) and the harnesses are attached (806) in their respectivelocations. Optionally, during the attachment (806), walls 242 and 244are mounted to a jig and/or any other assembly fixture, which allowsaccess to the interior of cage 230, while holding walls 242 and 244 inplace.

FIG. 7 shows cage 230 after some of harnesses 400 were mounted therein,while side wall 262 is still open. Side walls 262 are returned (808) totheir places and screws 270 are only partially tightened, in a mannerallowing movement within their respective holes.

Spine basket unit 208 is mounted (810) on first wall 242 and leaf basketunit 236 is mounted (810) on second wall 244. The leeway between firstwall 242 and second wall 244, due to screws 270 not being completelyfastened, ensures that the mounting of spine basket unit 208 on firstwall 242 does not affect the ability to properly align leaf basket unit236 on second wall 244, or vice versa. Screws 270 are then optionallytightly fastened (812), to allow for durability of director-class switch100 to movements and mounting of boards into the slots.

By constructing backplane 130 from harnesses 400, which are prepared inadvance, the assembly process is simplified. The wire connections areperformed outside of cage 230 which allows better work conditions.

It is noted that the assembly acts in FIG. 9 may be performed in otherorders. For example, spine basket unit 208 and/or leaf basket unit 236may be mounted on cage 230 before the mounting of some or all ofharnesses 400 within the cage.

Alternatives

As shown in FIG. 2, leaf slots 212 are arranged one in a row. In otherembodiments, multiple leaf slots are located on each row.

In the above description, each leaf board 118 is assumed to carry twoleaf switches 102. In other embodiments, each leaf switch 102 may be ona separate board or three or more switches may be mounted on a singleboard. In some embodiments, different boards may carry different numbersof switches. Accordingly in these embodiments, different slots havesizes for accommodating the boards they are intended to receive.

While the above description relates to a two-sided director-class switchin which spine boards 112 are mounted in slots on wall 242 which isopposite wall 244 against which leaf boards 102 are mounted, theprinciples discussed above may be used in other director-class switchlayouts. For example, stand-alone harnesses may be used to connect boardslots in a one sided switch, in which the spine boards 112 are mountedon the lower (or upper) half and the leaf boards are mounted on theupper (or lower) half. In this arrangement, the harnesses optionallyinclude longer cables to allow the connection between the upper andlower halves. In other example embodiments, a three or four sideddirector-class switch is used, and the harnesses connect the spine boardslots to the leaf board slots.

Furthermore, the term director-class switch is used herein to refer toswitches that have a relatively high port count, which benefits frombeing constructed from modular harnesses. These director-class switchesmay include more than 128 ports, more than 512 ports or even more than1024 ports. It is noted, however, that in some case embodiments of theinvention may be implemented on relatively small director-classswitches, including for example less than 512 ports, less than 256 portsor even less than 128 ports.

While in the above description each leaf switch matches three interfaceunits 248, and each cartridge 402 includes six interface port units 248,other numbers and arrangements may be used in accordance with thepresent invention. For example, each leaf board 102 may be designed tomatch only two interface port units of nine ports each, and thecartridges each include nine such interface units.

The number of internal ports 106 corresponding to a single leafinterface port unit 248 is optionally selected in a manner which reducesthe number of port units 248 in a suitable manner, without making thecartridges too large.

It will be appreciated that the embodiments described above are cited byway of example, and that the present disclosure is not limited to whathas been particularly shown and described hereinabove. Rather, the scopeof the present disclosure includes both combinations andsub-combinations of the various features described hereinabove, as wellas variations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description and which arenot disclosed in the prior art.

The invention claimed is:
 1. A main unit of a director-class switch,comprising: a chassis; a plurality of slots on the chassis configured toreceive switch boards; and a plurality of harnesses, each harnesscomprising: first and second rods; a plurality of interface port unitsmounted on each of the first and second rods; and cables connecting eachof the interface port units of the first rod to each of the interfaceport units of the second rod, wherein the entire harnesses including therods and the connecting cables are mounted in the chassis such that: theinterface port units face ends of the slots in a manner configured tomate with corresponding connectors of switch boards inserted into theslots, at least two of the plurality of interface port units are mountedin each slot, and at least two of the interface port units of each rodare located in different slots.
 2. The main unit of claim 1, wherein theplurality of slots are located on first and second opposite walls of thechassis.
 3. The main unit of claim 2, wherein the slots located on thefirst wall are configured to receive boards of a single type.
 4. Themain unit of claim 3, wherein the slots located on the first wall areconfigured to receive a different type of boards from the slots locatedon the second wall.
 5. The main unit of claim 2, wherein the first andsecond opposite walls of the chassis are connected by screws located inholes at least 50% larger than the cross-sections of the screws.
 6. Themain unit of claim 1, wherein each slot includes a plurality ofinterface port units of different harnesses.
 7. The main unit of claim1, wherein the plurality of harnesses include a first harness havingcables of a first set of lengths and a second harness having cables of asecond set of lengths different from the first set of lengths, allowingfor different maximal distances between the rods of the first and secondharnesses.
 8. The main unit of claim 1, comprising a printed circuitboard serving as a connection between a power source of thedirector-class switch and power sockets in each of the slots.
 9. Themain unit of claim 1, comprising power cables connecting a power sourceof the director-class switch to power sockets in each of the slots. 10.The main unit of claim 1, wherein the first and second rods comprisemetal rods.
 11. The method of claim 1, wherein the first and second rodscomprise rigid bars.
 12. The method of claim 1, wherein the plurality ofharnesses includes a first harness whose first and second rods aremounted in the chassis at a same height, and a second harness whosefirst and second rods are mounted in the chassis at different heights.13. The method of claim 1, wherein the plurality of harnesses includes afirst harness mounted in the chassis with a first height differencebetween the first and second rods of the first harness, and a secondharness mounted in the chassis with a second height difference betweenthe first and second rods of the second harness, wherein the secondheight difference is different from the first height difference.
 14. Amethod of constructing a main unit of a director-class switch,comprising: providing a chassis including a plurality of slots on thechassis configured to receive switch boards; providing a plurality ofharnesses, each harness comprising: first and second rods; a pluralityof interface port units mounted on each of the first and second rods;and cables connecting each of the interface port units of the first rodto each of the interface port units of the second rod, mounting theharnesses in the chassis such that the interface port units face ends ofthe slots in a manner configured to mate with corresponding connectorsof switch boards inserted into the slots, wherein at least two of theplurality of interface port units are mounted in each slot, and at leasttwo of the interface port units of each rod are located in differentslots.
 15. The method of claim 14, wherein providing the chassiscomprises providing a chassis with walls connected to each other in amanner allowing limited relative movement.
 16. The method of claim 15,comprising strengthening a connection between the walls, limiting thepossibility of relative movement of the walls, after mounting theharnesses in the chassis.
 17. The method of claim 14, wherein theplurality of harnesses includes harnesses having different cables ofdifferent lengths allowing for different maximal distances between therods of the harness.
 18. The method of claim 14, wherein the harnessesall include the same number of interface port units.
 19. The method ofclaim 14, wherein each of the rods of the harnesses comprises at leastfour interface port units.